From: Steve Harris <sbharris@ix.netcom.com>
Newsgroups: rec.audio.pro,sci.electronics.design,sci.med
Subject: Re: Speakers for High Frequency Sound
Date: 11 Feb 2005 18:39:02 -0800
Message-ID: <1108175942.790485.317700@c13g2000cwb.googlegroups.com>

I can't answer question 1.

Question #2 is hard, because 16 kHz is at the edge of hearing, and that
edge is heavily volume and age-dependent. Transmission of this stuff is
dependent on the flexibility of your earbone joints, which craps out
with age. So you see the same dependence and variability as you do in
gymnastics, and for the same reasons. The older you are, the less
likely you are to be able to detect high frequency at a given volume.
But there are no firm limits.

Interestingly, your cochlea can hear tremendously high frequencies well
into "ultrasound" above 20 kHz, so long as they are gotten in by bone
conduction (putting the transducer on your skull). It's the earbones
that are the block. Perhaps there are some people who have particularly
good skull connections to their inner ear.

Question #3. Is related to why transformers and many other devices hum
with the frequency of the energizing AC. The variable magnetic field
generated by the coil causes Lorenz forces on the other wires of the
coil, just as in a motor. They flex, and if they're not tacked down
well, they vibrate. Air picks that up.

SBH